Electrical Conductivity (EC)
The two most important factors in nutrient and water management are conductivity and pH, and a good understanding of these variables is essential for successful hydroponic gardening.
The conductivity of a solution is an expression of the capacity of that solution to conduct an electric current. Distilled or de-ionised water will conduct virtually no electricity at all and therefore will have a conductivity reading of zero. As salts are dissolved in the water so the conductivity of the solution increases. The conductivity of a nutrient solution is therefore a measurement of its “strength” as indicated by the actual amount of salts dissolved.
What is Electrical Conductivity in hydroponics?
In hydroponics all nutrients are made of mineral salts, which are dissolved into water, and the strength of the nutrient solutions can be detected by an electrical conductivity (EC) meter. The higher the ionic (salt) concentration, the higher the level of EC, hence EC can be used as an indicator of the strength of a solution. EC meters consist of two electrodes spaced 1 centimetre apart, which are placed in the solution to be measured.
When power is supplied to the meter, an electrical current passes from one electrode through the solution to the other electrode, and the meter displays how much electrical current is flowing between the electrodes and shows it as EC. These meters work on the principle that an electrical current is conducted more easily as the concentration of nutrient salts in a solution increases.
Why is EC important?
Knowing the EC of the feed solution is important because it gives the grower an indication of the strength of the solution and how plant growth is affected by the nutrient level. Different plants grow well at different levels of nutrient strength, and it is important to control this nutrient strength to provide the optimal conditions in the root zone, which in turn allows the maximum uptake of the nutrients into the rest of the plant’s cellular structure.
Units of Measure
Electrical conductivity can be expressed using a number of different units but the international standard is EC, and the unit of measurement is usually milliSiemens or microSiemens. The difference between these two units of measurement is the placement of the decimal point, so 1 milliSiemens is equal to 1000 microSiemen. The important thing to remember is that a nutrient solution at “full strength” (according to the manufacturer’s directions) has an EC between 2-2.5 milliSiemens and is expressed as 2mS/cm.
Sometimes EC is expressed in other units of measurement, such as CF and TDS/ppm. CF (conductivity factor) is basically EC multiplied by 10, and is used in some places because it eliminates the need for a decimal point, so an EC of 0.1 is equal to a CF of 1. TDS (total dissolved salts) and PPM (parts per million) are commonly used in the United States, and the meter used for this is actually an EC meter, which has an internal correction factor that converts the EC to the TDS readout.Unfortunately, this is where it becomes complicated as different meters have different correction factors, usually dependent upon the industry in which they are used.
- The first problem is that some meters use a factor or 500 ppm per mS/cm and others use 700 ppm per mS/cm.
- The second problem and more importantly, is that different salts have a different capacity to conduct electricity, so two solutions made up at 1,000 ppm with different salts would have quite different readings on an EC meter or a ppm meter.
For these reasons it is recommended that growers use an EC meter and avoid using TDS meters. It is important to know that EC will measure the strength of a nutrient solution, but it cannot measure the nutrient balance of that solution. Also, EC does not measure any non-ionic components in the solution, and when using organic fertilisers, the solution strength will be higher than indicated by its EC, because most carbon-based compounds are not ionic and will not register on an EC meter.